1. Field of Invention
This invention relates generally to a video signal processing circuit used in a video signal reproducing apparatus, and is more particularly directed to a video signal processing circuit having an analog-to-digital converter for converting a reproduced video signal to a digital video signal.
2. Description of the Prior Art
The goal of getting a high definition television picture, using a high definition video system (HDVS), which processes the wide band video signal with increased scanning lines, has developed in recent years.
In the video tape recorder which records or reproduces the wide band video signal used in said HDVS, it has been tried to record said wide band one field signal in the same way as in the former video tape recorder, with one field signal in the same way as in the former video tape recorder, in which one field video signal is recorded in only one track. The result is that the diameter of head drum becomes a few times larger than usual, so it is not practical. Segment recording or multi-channel recording, could be used in which the wide band, one field signal would be recorded into plural tracks by being divided into plural segments.
In said multi-channel recording, for example, by dividing the wide band video signal into two channels in the recording process, the video signal of each channel is time base expanded, frequency modulated, and recorded into the recording media. In the reproducing process, each channel video signal reproduced from the recording media is frequency demodulated, time base compressed respectively, and as an original video signal corresponding to one channel is reproduced. Furthermore, said time base expanding and time base compression are processed digitally, wherein the video signal is digitized.
By the way, in the recording system of a video tape recorder which employs multi-channel recording, the most important factor determining the definition of a reproducing signal is whether there are level differences and linearity differences between channels, especially in the case of analog recording. After the video signal which was divided into several channels is processed independently with the demodulating circuit, video amplifier, analog-to-digital converter etc. which exist in each channel, said divided video signal will be reconstructed into the corresponding single channel video signal. There was the difference of signal level and signal linearity in the processing each circuits of channel, for example, in case of the same video signal was recorded and reproduced, there was the difference between the signal from each channel. This is the one of the causes for loss of definition of a reproduced video signal.